Showing papers on "Variable-frequency drive published in 2003"

Energy reduction process and interface for open or closed loop fluid systems with or without filters

Abstract: A Process and Interface to reduce the energy required to operate a swimming pool pump. The process improves the conventional process by causing the pump to vary its operation based on variable filter loading conditions. The process uses a flow sensor to send a signal to the interface which then signals a variable frequency drive to increase or decrease the speed of the pump motor in compliance with user programmed flow. The pump operates at reduced energy until the filter load increases due to captured debris. As the filter load increases, the pump speed increases.

Refrigerant cooled variable frequency drive and method for using same

Abstract: A method for operating a vapor compression system having a compressor driven by a variable frequency drive, wherein the compressor feeds a refrigerant loop, wherein the refrigerant loop includes a cooling circuit for the variable frequency drive, and wherein a flow control member is positioned for controlling flow of refrigerant from the refrigerant loop to the cooling circuit including the steps of: sensing an operating temperature of the variable frequency drive; and controlling the flow control member based upon the operating temperature.

Method of cutting carbon and alloy steel

Abstract: The present invention discloses a method and apparatus for controlling the load on the blade or spindle motor of a steel-cutting saw for optimizing blade life, while at the same time reducing cutting cycle time and protecting the blade, gearbox and spindle hub from stresses caused by binding and jamming of the blade while cutting into a steel member. Using a programmable logic controller (PLC) to implement the method, the load current drawn by the spindle motor is sensed and compared to a reference value representing the desired optimum operating current. As the saw cuts through a steel member, variations in hardness cause the spindle motor current to fluctuate accordingly. The blade is advanced into the steel member by an electric servomotor. The rate of advancement of the blade is controlled by the PLC. As the current on the spindle motor increases, the PLC is programmed to reduce the rate of advancement of the blade, thereby reducing the load on the blade. The blade loading and spindle current are directly proportional. The rotational speed (RPM) of the blade is also maintained constant by a variable frequency motor drive that powers the spindle motor. The PLC does not vary the RPM of the blade. The operator selects the blade speed as a value in the range from 3 to 85 RPM, which is the reference value maintained by the variable frequency drive. The feed rate is the variable that is controlled by the PLC, by which the load current of the spindle motor is maintained relatively constant. The PLC also compares the current to a preset maximum value, normally around eighty percent of full load amps of the spindle motor. Upon reaching the preset maximum, the PLC removes the run command signal to the variable frequency drive, causing the spindle motor to stop abruptly. Response time for clearing an overload condition is approximately 10 milliseconds, or one-tenth of the time required to clear the overload using conventional analog current sensing and shut-off devices.

Irradiation facility control system

Abstract: The present invention is directed to an article irradiation facility that comprises, within a cell, an accelerator for generating a radiation beam and a beam pass conveyor. In order to better control the dose delivered to articles treated at the facility, the current of the radiation beam is slaved to the speed of the beam pass conveyor. The actual (versus requested) speed of the beam pass conveyor is continuously monitored using a variable frequency drive. The drive infers the speed of the beam pass conveyor from changes in the induction, resistance, flux current and/or inertia off the motor for the beam pass conveyor. The drive is positioned outside the cell and eliminates the need for speed sensors within the cell that are susceptible to radiation damage.

Control system and method for an overhead bridge crane

Abstract: Included herein is a system and method for controlling a velocity vector of an overhead crane. A motor is attached to the crane and is positioned to move the overhead crane and has an output vector including a rotational direction and a rotational speed. A variable frequency drive is positioned to transfer voltage and current at a frequency to the motor. A processing unit converts the output vector to an amount of voltage and current at a given frequency and can instruct the variable frequency drive to send a frequency to the motor at a frequency substantially equal to the frequency at which the motor is presently rotating. This creates a speed match for the motor reducing spikes during operation of the motor and substantially eliminates open circuit decay. A hydraulic brake operates in connection with the processing unit and the variable frequency drive to slow the crane without driving the motor into the brake.

Modelling and identification for reduction of overvoltage transients

Abstract: The main problems that appear when using a long cable connection between a variable frequency drive (VFD) and the AC motor are overvoltages and bearing currents. The latter concerns especially EMC, while the overvoltage transients can be fatal to the motor. The ‘converter–cable–motor’ system behaviour concerning overvoltages is investigated and then an on-line identification of the cable parameters is proposed. This result could be used to reduce overvoltages. An algorithm is introduced that decreases the amplitude of the adverse overvoltage effect. The algorithm is based on the modification of the applied PWM pattern.

Clean power powerbus variable frequency drive system

Abstract: A N pulse variable frequency drive for driving two or more motors that is the combination of two or more variable frequency drives with each drive driving an associated one of the two motors One application is a decanter centrifuge which has a main motor to drive the bowl and a back motor to drive the conveyor One of the two variable frequency drives drives the main motor and the other drive drives the back motor The variable frequency drives are connected to a common buss and to a N pulse phase shifting transformer